Rotary wing aircraft, especially helicopters, are distinguished, among other vehicles, by their ability to lift and transport heavy loads to locations that are not easily accessible by conventional means. A special type of transport in this case constitutes the sling load transport where the load is fastened by means of a supporting cable or wire harness support in the form of a net attached to one or more hooks on the helicopter or on an external winch. However, the attaching of a sling load to a helicopter changes the system dynamics and degrades the flight characteristics. Additionally, the flight control task of the pilot is increased as he also must control the sling load since the complexity to the flying entire system is increased by the sling load. This ultimately leads to increased stress for the pilot and generally causes a reduction in flight safety.
During sling load transport there is risk of uncontrollable, low-frequency pendulum motions as a result of aerodynamic interference or control inputs. The pendulum motion can turn into unstable pendulations which can also be provoked by pilot inputs. This can eventually lead to pendulations provoked by the pilot. The pilots can perceive the dynamic influence of a pendulating sling load from the helicopter, but usually they can't see the sling load, thus there is risk that in certain cases the corrective control inputs from the pilot to dampen the overall system do actually provoke the pendulum motion even further. The reason for this is that the pilot intuitively is trying to counteract the transverse force exerted on the helicopter caused by the pendulating sling load, instead of flying to a limited extent behind it in order to release the sling load of transverse forces. Heavy pendulations from the sling load endanger the entire system and its crew as their impact on the helicopter may lead to the fact that the helicopter can no longer be controlled.